@thomasfuchs @glennf Agreed! I personally only use heat pumps here in North Alabama. However, one of my houses has a combination system with gas heat, rather than resistive elements.

@thomasfuchs @glennf Sure you may have full heat output down to 5°F. However, the thermodynamic balance point typically is somewhere between 10 and 20°F. This is the point where the heat pump, i.e. the heat engine running in reverse, requires more energy than a resistive heating element to heat the air. The second law of thermodynamics seems always to get in the way!

@thomasfuchs @glennf Implying that heat pumps don't work was obviously was not my intention! As a physics professor, I know about thermodynamics. I was trying to point out that heat pumps are best suited to work as air conditioners and as heat for milder climates. In colder climates you may want a combination system that switches to a furnace when it gets cold.

@glennf @thomasfuchs Using a heat pump to heat is OK in a temperate climate. However, here in the Southeast we tend to have several cold snaps every year. By cold snap I mean when temperatures go below 20F. At this point an air-2-air heat pump (as opposed to a "geothermal" ground-2-air heat pump) cannot extract enough energy from the outside air to heat the building. I found this out the hard way when the circuit breaker for the resistive heating element failed.

@mattblaze I always remember how small the first generation of wind turbines at Altamont pass were in comparison with subsequent generations. The physics is clearly favoring larger impellers, all constrained by materials engineering.

@siracusa I still have Inside Macintosh, Volumes I-VI sitting on the shelf. Rather dusty!

@petergleick As I boosted this, my computer started playing St. Stephen... (from The Closing of Winterland)